Six Sigma is a quality management programme to achieve "six sigma" levels of quality. It was pioneered by Motorola in the mid-1980s and has spread to many other manufacturing companies.

Six Sigma aims to have the total number of failures in quality, or
customer satisfaction, occur beyond the sixth sigma of likelihood in a normal distribution of customers. Here sigma stands for a step of
one standard deviation and corresponds in practice to fewer than 3.4 defects in one million.

That is, fewer than four in one million customers will have a legitimate issue with the company's products and service.

Many people believed that six-sigma quality was impossible, and settled for three to four sigmas. However market leaders have measurably reached six sigmas in numerous processes.